KTP crystal is mostly used as nonlinear crystals for frequency doubling of solid-state Nd:YAG crystal or Nd:YVO4 crystal laser, as it has large nonlinear optical coefficients, wide angular bandwidth and small walk-off angle, broad temperature and spectral bandwidth.

Hastings triplets achromatic lenses are designed to provide an infinite conjugate ratio and are useful for focusing collimated beams and for magnification. Steinheil triplets achromatic lenses are designed to provide a finite conjugate ratio and 1:1 imaging.